Bug 7132378

Bug Description:

This is a race bug.
The expected exception is a NullpointerException.
More details about this bug are at JDK-7132378 JIRA page.

Interleaving Description:

java.util.concurrent.FutureTask$Sync

t1  t2  V innerGet() throws InterruptedException, ExecutionException {
2           acquireSharedInterruptibly(0);
            if (getState() == CANCELLED)
                throw new CancellationException();
            if (exception != null)
                throw new ExecutionException(exception);
3           return result;
        }
        
        void innerSet(V v) {
            for (;;) {
                int s = getState();
                if (s == RAN)
                    return;
                if (s == CANCELLED) {
                    // aggressively release to set runner to null,
                    // in case we are racing with a cancel request
                    // that will try to interrupt runner
                    releaseShared(0);
                    return;
                }
    1           if (compareAndSetState(s, RAN)) {
    4               result = v;
                    releaseShared(0);
                    done();
                    return;
                }
            }
        }

Preconditions:
FuturnTask is not run.

a) thread 1 sets a value. It updates the task state to RAN at 1.
b) context switched, thread 2 acquires a continue signal at 2. The task state has been set to RAN at step a). So here thread 2 does not need to wait at 2.
c) thread 2 returns return that is null at 3.
d) context switched, thread 1 assigns a value to result. But unexpected null value has been returned at step c).

How To Reproduce:

This bug is reproduced under JDK 1.7.0.
It started at JDK 1.7.0, and has been fixed since JDK 1.7.0_40.
Execute the following scripts to run the test to reproduce the bug (assume the location of the jdk7 test project is jdk7_test_home).

Linux:
${jdk7_test_home}/scripts/7132378.sh [--javaloc path]
Windows:
%jdk7_test_home%\scripts\7132378.bat [--javaloc path]